Diaphragm Forces Due to Live Load
Diaphragm Forces Due to Live Load
(OP)
Hello All,
I have encountered a few structures which are racking back-and-fourth due to live loads (mostly pin-pin connection deck columns which were field built). I know many different ways of dealing with it structurally, but haven't found many resources for actually putting numbers to it.
Anyone have anywhere to point me to / ways you actually quantify this? Thanks.
I have encountered a few structures which are racking back-and-fourth due to live loads (mostly pin-pin connection deck columns which were field built). I know many different ways of dealing with it structurally, but haven't found many resources for actually putting numbers to it.
Anyone have anywhere to point me to / ways you actually quantify this? Thanks.






RE: Diaphragm Forces Due to Live Load
Mike McCann, PE, SE (WA)
RE: Diaphragm Forces Due to Live Load
You get that thing up to full occupancy loading and everyone does the time warp, it is going to start AND end with the jump to the left.
Built completely by Part 9 specs by framers, no eng involvement except from geotech for screw pile installation on the structure (30' long, 10' spans, 8' joists w/ 1'6 overhang).
RE: Diaphragm Forces Due to Live Load
Mike McCann, PE, SE (WA)
RE: Diaphragm Forces Due to Live Load
RE: Diaphragm Forces Due to Live Load
The same as for non-building structures. After all, humans are not buildings, but they are structures, right?
Seriously, I have taken this approach too in the past and been accepted.
Mike McCann, PE, SE (WA)
RE: Diaphragm Forces Due to Live Load
Dave
Thaidavid
RE: Diaphragm Forces Due to Live Load
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Diaphragm Forces Due to Live Load
Fwiw I usually design all mezzanine for 10% of the live load as a notional load.
RE: Diaphragm Forces Due to Live Load
RE: Diaphragm Forces Due to Live Load
Trangled: The is exactly what I was looking for, thanks.
Kootk / Jay: Exactly the problem here, the homeowner actually went ahead and manufactured some thick water cut T and L brackets for post and beam connection that did a bit of help but there is still a stiffness issue at the base where the columns meet the supporting screw piles in a pinned connection. I know the, 'It has worked in the past' solution, just started to get on my nerves that I did't have much in the ways of quantifying it.
David: Gonna have to find a way to expense that standard... 'I am running a quote for a stadium project' sounds like a good line. Thanks haha.
Edit. To summarize the report from Trangled:
-12psf (plan area) lateral load is a good design assumption (based on 40lbs live for cyclic; 10lbs live for impulse loading)
-Unzipping at the ledger board wasn't an issue (surprising)
-Nails shouldn't be used for ledger boards due to withdraw loading (unsurprising)
They exclude decks with a larger than 1:1 ledgerboard length: deck length; makes sense.
RE: Diaphragm Forces Due to Live Load
Is there a good tension load path in the connection to take the moment coming out of the diaphragm? I feel like that's the most likely culprit.
Regardless of the cause, the best way to deal with it is to put braces on your posts, or at least little knee braces to turn it into a moment frame. Then you're just passing pure lateral shear into the two baylines.
I use the same 10% that jayrod uses. It's a strength level that doesn't usually require more than a nominal cost and it ensures you're actually checking it. I've dropped below that before, but it's my starting point.
RE: Diaphragm Forces Due to Live Load
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.